MIDI Note Number Chart for iOS Music Apps

Greg Cerveny
1 min readSep 27, 2017
Middle C = C4, the default implementation for the iOS audio sampler unit

I’m regularly pulling this little chart up as I build music apps. I use it to translate scales and chords to numbers and to figure out what to name my samples.

Middle C in iOS

Middle C, in MIDI, is note number 60. Whether that note translates to C3 or C4 varies based on the platform.

With iOS and Apple’s sampler audio unit AVAudioSamplerUnit, middle C is C4.

Impact of Middle C = C4

Apple’s sampler audio unit will automatically associate a sample to a MIDI note number based on the name of the audio file. This is where middle C = C4 becomes important.

If you have an audio file named piano_C4.wav, and you load it into a sampler with sampler.loadAudioFiles(at: audioFileURLs), it’ll automatically get mapped to note number 60.

To trigger the sample is just: sampler.startNote(60, withVelocity: 127, onChannel: 0).